Re: [PATCH] add boot option to control Intel combined mode behavior (to allow DMA in combined mode configs!)

From: Jeff Garzik (jgarzik_at_pobox.com)
Date: 11/29/05

  • Next message: Tarkan Erimer: "Re: [BUG]: Software compiling occasionlly hangs under 2.6.15-rc1/rc2 and 2.6.15-rc1-mm2" 
    Date:	Tue, 29 Nov 2005 16:54:21 -0500
To: Jesse Barnes <jbarnes@virtuousgeek.org>

    Jesse Barnes wrote:
    > Combined mode sucks. Especially when both libata and the legacy IDE
    > drivers try to drive ports on the same device, since that makes DMA
    > rather difficult.
    >
    > This patch addresses the problem by allowing the user to control which
    > driver binds to the ports in a combined mode configuration. In many
    > cases, they'll probably want the libata driver to control both ports
    > since it can use DMA for talking with ATAPI devices (when
    > libata.atapi_enabled=1 of course). It also allows the user to get old
    > school behavior by letting the legacy IDE driver bind to both ports.
    > But neither is forced, the patch doesn't change current behavior unless
    > one of intel_combined_mode=ide or intel_combined_mode=libata is passed
    > on the boot line. Either of those options may require you to access
    > your devices via different device nodes (/dev/hd* in the ide case
    > and /dev/sd* in the libata case), though of course if you have udev
    > installed nicely you may not notice anything. :)
    >
    > Let me know if the documentation is too cryptic, I'd be happy to expand
    > on it if necessary. I think most users will want to boot with
    > 'intel_combined_mode=libata' and add 'options libata atapi_enabled=1'
    > to their modules.conf to get good DVD playing and disk behavior
    > (haven't tested CD or DVD writing though).
    >
    > Documentation/kernel-parameters.txt | 7 +++++++
    > drivers/pci/quirks.c | 30 ++++++++++++++++++++++++++++
    >
    > I'd much rather things behave sanely by default (i.e. DMA for devices on
    > both ports), but apparently that's difficult given the various chip
    > bugs and hardware configs out there (not to mention that people's
    > drives may suddenly change from /dev/hdc to /dev/sdb), so this boot
    > option may be the correct long term fix.
    >
    > Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>

    Seems like it should work. I presume you tested this?

    Remove the 'intel_' prefix from the kernel parameter, since this concept
    applies to other controllers as well. Otherwise, seems OK.

            Jeff

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